Physico-chemical characterization of the blow-fly storage protein calliphorin has been undertaken. The reversible monomeric-hexameric state of the protein has been studied as a function of pH and salt concentration, and intermediate oligomers "trapped" by use of cross-linking reagents or by chemical modification of specific protein groups. The conformational state of the protein has been examined by circular dichroism and difference spectroscopy. A variety of "state of the art" physical separation methods has been used in unsuccessful attempts to isolate pure, single calliphorin monomers and/or hexamers. Radioactive calliphorin was employed in preliminary experiments to determine the fate of the injected protein during metamorphosis.